1. Field of the Invention
This invention relates to a printing apparatus, and more particularly to a document-feeding roller mechanism and a printing apparatus having the same and being capable of adjusting the document clamping force.
2. Description of the Related Art
In a conventional printing apparatus, a document is clamped and conveyed by a feeding roller assembly to move through a printing module, and is ejected from the printing apparatus by a document-ejecting roller assembly disposed downstream of the printing module. During feeding of the document, the feeding roller assembly provides a clamping force to the document for pushing and moving the document toward the printing module.
While the document is passing through the printing module, since leading and trailing ends of the document are clamped by the feeding roller assembly and the document-ejecting roller assembly, respectively, the document is subjected to a pulling force. When the trailing end of the document is removed from the feeding roller assembly, the pulling force applied to the document disappears due to release of the clamping force of the feeding roller assembly, thereby resulting in a change in the document tension. Such a sudden tension change affects adversely the printing quality.
Moreover, since the clamping force of the feeding roller assembly to the document is fixed, in case of power failure occurring during a printing process, it is difficult to remove a document jammed in the feeding roller assembly from the conventional printing apparatus.